Conflicting use of PublicRoomsChunk for space hierarchy over federation

[Kladki]

Link to problem area:
https://spec.matrix.org/v1.9/server-server-api/#get_matrixfederationv1hierarchyroomid

Issue
There are two different types with the name PublicRoomsChunk, with the only difference being that the latter has a children_state field which the other doesn't. In ruma, it is assumed that the former is for the children field, and the latter is for the room field. However, in the example request in the spec, both the children and room fields use the children_state field, so it is unclear whether the example is correct and they should both have the children_field, ruma is correct and only the room field should have that, or even maybe the children field should have that and the room field shouldn't.
Either way, they really should either be merged (for the former solution), or have different names (for the others).

[deepbluev7]

According to the openapi spec, only room should have that field: https://github.com/matrix-org/matrix-spec/blob/c4e69d8cb15c3442484e988a83dc85d749423caa/data/api/server-server/space_hierarchy.yaml

[zecakeh]

It seems like the types are indeed supposed to be different:

1. MSC2946 says:

   children_state: As per Client-Server API version, though only on the room and not children.

2. In the Synapse implementation, there is a comment that says explicitely that the children_state is not set on children items: https://github.com/element-hq/synapse/blob/274f289a52a0097784d7179c1d912dbc3cfda3ee/synapse/handlers/room_summary.py#L402-L403

[clokep]

There are two different types with the name PublicRoomsChunk

There's also a third use under the public rooms API, I don't know if this causes issues or not but is certainly confusing.